Pulse repeater employing alternately conducting devices responsive to control means alternately priming and cutting-off said devices



Nov. 24, 1964 D. A. BREWIN 3,158,814

PULSE REPEATER EMPLOYING ALTERNATELY CONDUCTING DEVICES RESPONSIVE TOCONTROL MEANS ALTERNATELY PRIMING AND CUTTING-OFF SAID DEVICES FiledJan. 16, 1965 2 Sheets-Sheet l 65V. PULSE 42| 20 I40 I42 '23 SOURCE I30I45 A OAB V 503 502 |2| A 221 EAB INVENTOR. DONALD A. BREW/IV g M WJQZZJ{QENT 245 EP i 220 230 223 244 PULSE REPEATER EMPLUYENG ALTERNATELYCONDUCTHNG DEVECES RESPONSKVE T CQN- TROLL MEANS ALTERNATELY PRIMING ANDCUlTTiNG-QFF SAliD DEVICES Donald A. iirewin, Rochester, N.Y., assignorto General Dynamics Corporation, Rochester, N.Y., a corporation ofDelaware Filed Jan. 16, 1963, Sci. No. 251,796 11 Claims. (Cl. 328-210)This invention relates in general to a pulse repeater and, moreparticularly, to a pulse repeater for driving a counter with increasedaccuracy.

Although the invention herein disclosed is suitable for more generalapplication, it is particularly adapted for use in a system wherein itis necessary to count the number of pulses in a group of a first typewhich occur between pulses of a second type. For example, in tollticketing telephone systems, information relating to a call isfrequently transmitted as a coded series of first pulses separated by adistinctive second pulse. In systems such as that disclosed in PatentNo. 2,877,311 to Morris et al., the first and second types of pulses arereferred to as mark and space pulses, respectively. Experience has shownthat a very satisfactory way to count groups of pulses of the typedescribed is to use the input pulses to alternately operate, or fire,first and second tubes in a driver circuit. The driver circuit, in turn,provides output signals to a counting circuit which typically cornprisesa chain of cold cathode gas tubes which are arranged in odd and evengroups.

The effectiveness of the extinguishing action in the prior art circuitswas reduced by the connection of the counting chain to the drivercircuit. Furthermore, the prior art circuit required a potentialclamping circuit to eliminate the production of a current spike from theload and the clamping circuit further reduced the effectiveness of thedriver extinguishing circuit.

Accordingly, it is the general object ofv this invention to provide anew and improved counting circuit driver.

It is another object of this invention to provide a new and improvedcounting circuit driver wherein the load does not affect theextinguishing action.

It is another object ofthis invention to provide a new and improvedcounting driver circuit comprising a pair of tubes which are firedalternately and which are preextinguished.

It is another object of this invention to provide a new and improvedcounting driver circuit comprising a pair of cold cathode gas tubeswhich are fired alternately and wherein the extinguishing of one tubedoes not depend upon the firing of the other tube.

in accordance with a preferred embodiment of the present invention, thecounting circuit driver comprises twocold cathode gas tubes and abistable device. The input pulses which are to be counted by thecounting chain driven by the driver are applied to the control anode ofboth of said gas tubes. The bistable device enables the tubesalternately and is shifted from one to the other of its bistable statesas each of the gas tubes fires. Thus, when the enabled tube is fired byan input pulse,,the bistable device is operated, thereby removing theenabling potential from the fired tube and pre-extinguishing it. Theenabling potential is thereupon applied to the other tube. Accordingly,the fired tube is pre-extinguished and,

3,158,814 Patented Nov. 24, 1964 therefore, does not need to be put outwhen the other tube fires. This permits a more accurate count withouteither introducing an unwanted spike into the load circuit or having theeffectiveness of the extinguishing circuit be reduced by the loadcircuit, as in prior art counting circuit drivers.

Further objects and advantages of the invention will become apparent asthe following description proceeds, and features of novelty whichcharacterize the invention will be pointed out in particularity in theclaims annexed to and forming a part. of this specification.

For a better understanding of the invention, reference may be had to theaccompanying drawings in which:

FIG. 1 illustrates a counting circuit driver incorporating theinvention; and

FIG. 2 illustrates a typical counting circuit driven by the driver.

It is to be understood that only the details of the circuit necessary tounderstand the invention have been shown. For example, the means forproducing the first and second types of pulses has not been shown. Thesepulses could be derived from many sources. For example, the first typeof pulse could be activated by a typical counter mechanism, such as atrafiic counter, while the second pulse might be activated at fixed timeintervals so that the number of counts per unit time could be readilydetermined; or the first and secondpulses may be indicative of mark andspace pulses, respectively, as read from a toll ticketing tape recorder,as described in the above cited Morris et al. patent. In addition, onlya typical counter is shown. it will be appreciated that, depending uponwhat is being counted and the need for registering the count, that oneor more counters and/ or registers may be required and that a steeringcircuit may be employed to steer the output signals from the driver orof pulses is subsequently transferred, in coded form, to a selected oneof a plurality of registers.

It is believed that the operation of the invention can best beunderstood by considering the following detailed description inconjunction with the accompanying figures. The tubes ill, 222, 4%, andthe tubes of FIG. 2 may be cold cathode gas tubes, such as RCA type5823.These tubes have a starter anode-to-cathode breakdown volt age ofapproximately seventy-three volts minimum and an anode-to-cathodepotential drop of approximately sixty volts. However, as the tube ages,this potential may increase. In addition, there is included in FIG. 1 abistable device 5ii having contacts 5&2 and 503 which may be mercurywetted. Current in one direction through coil 5% will cause contacts 592to close, while current in the other direction through coil Silt) willcause contacts 5% to close. Either set of contacts, once closed, willremain closed even though the current in coil 50%) ceases to flow. Uponreversal of a direction of current in coil 50%, the contacts 502 and5423 will reverse themselves, that is, the closed contacts will open andthe open contacts will close. The operation of the counting drivercircuit will not be afiected by whether or not the contacts 502 and 503are bridging contacts.

All terminals marked are connected together and to the reference orsystem ground. Accordingly, these terminals will hereinafter be referredto as ground. The terminals marked are connected to a potential which I3 is sixty-five volts positive with respect to ground. The terminalmarked B+ is at a positive potential of one hundred and sixty-five voltswith respect to ground.

As will be seen, it Will be convenient to refer to tubes ill and 222 asthe odd and even tubes, respectively. Ac cordingly, these tubes havebeen given distinctive odd and even numbers to facilitate theassociation of their function with their designation. In addition,elements Whose functions are most closely associated with tube 111 havebeen given designations starting with the digit 1; While elements whosefunctions are most closely associated with tube 222 have been givendesignations starting with the digit 2. in a similar manner, elementswhich are most closely associated with tube dill have been givendesignations starting with the digit 4.

It will be observed that while contacts see are closed, the B+ potentialwill be applied through the common load resistor 221 to the leaddesignated EAB (even anode bus). In a similar mannenwhen contacts 5t)?are closed, the B+ potential will be applied through the common loadresistor 121 to the lead designated GAB (odd anode bus).

When contacts 503 are open, it will be seen that capacitor 130 isdischarged as the two sides thereof are connected to ground throughresistors 12% and 123, respec tively. Later, when contacts 5% close, theleft terminal of capacitor 136 will be suddenly raised to the 3-}-potential. Capacitor 134) will charge to a potential of plus sixty-fivevolts, the potential connected to the cathode of diode 142. Accordingly,a sixty-five volt pulse is applied to the OP (odd pulse) lead inresponse to the closing of contacts 503. In a similar manner, it will beobvious that capacitor 2% performs in the same manner to apply asixty-five volt pulse to the EP (even pulse) lead when contacts 502close.

As will be seen, the tubes 111 and 222 respond alternately to successivepulses on lead MK and the circuit is reset in response to each pulse onthe lead designated Si irrespective of which of the two tubes 111 or 222was last fired. The pulses applied to the MK lead will be applied to thestarter anodes of both the odd and even tubes and pulses applied to theSP lead will be applied to the starter anodes of the even tube and theauxiliary tube designated 222 and 4%, respectively. In addition, the SPpulse is applied to the Reset lead of the counter circuit of FIG. 2through capacitor 433.

t will be assumed that no tube of FIG. 1 is fired and that contacts Sillare closed, thereby applying a 13-}- potential to the anode A of tube111 at the time that the first pulse appears on the MK lead. As will beseen, this is the condition which prevails after the receipt of an SPpulse. The application of a sixty-five volt pulse to the MK lead willcause a sixty-five volt pulse to be passed through capacitors 216 and116 to raise the potentials of the starter anodes of tubes 222 and 111,respectively, to approximately one hundred and thirty volts since theyare biased to sixty-five volts by resistors M22 and sea. Since a B+potential is connected to the anode A of tube 111 and its cathode K isat ground potential, tube 111 will be fired, thereby raising its cathodeterminal to a potential of approximately one hundred volts. The cathodepoten tial will be equal to the B+ potential minus the anode-tocathodepotential of the tube, which is approximately sixty volts, and minus thepotential drop in resistor 195. Tube 222 will not be fired as its anodeis at ground potential. The one hundred volt positive potential on thecathode oftube ill will cause a current to flow in the operating coil ofbistable relay Still. The circuit is comand 222.

The application of the 13-}- potential to the anode of tube 222 does notcause tube 222 to be fired at this time as the pulse from the MK leadhas been dissipated and the starter anode of tube 222 has been returnedto sixtyfive volts, a potentail which is below the firing potential.

The application of the 13-}- potential to the DAB lead will apply the B+potential through the common load resistor 12?; to the anodes of the oddtubes of FIG. 2, as will be described later. In addition, a sixty-fivevolt pulse will be applied to the OP lead, as mentioned before, and, aswill be shown, this pulse will be used to fire the first odd tube of thecounting chain of HG. 2. Accordingly, when a steady state condition hasbeen reached after the first MK pulse, none of the tubes of FIG. 1 willremain fired, but contacts 5% will remain closed.

The next sixty-five volt pulse to be applied to the MK lead will againbe applied to the starter anodes of both the odd and even tubes.However, since only the even tube 222 has a 13+ potential applied to itsanode, only this tube will be fired. In response to the firing of tube222, its cathode will be raised to approximately one-hundred volts and,therefore, a current will flow through resistor Sill and relay coil 50%,thereby operating the relay and causing contacts 5% to open and contacts592 to close. The opening of contacts 563 will extinguish tube 222 and eclosing of contacts Sill will re-apply the B+ potential to tube 111,thereby preparing it to fire upon receipt of the next sixty-five voltpulse on the MKlead. In a manner similar'to that already described, theclosure of contacts 5% will apply the B+ potential through the commonload resistor 221 to the EAB lead and a sixty-five volt pulse will beapplied to the EP lead to fire the first even tube in the counting chainof FIG. 2, as will be described below.

The operation continues in the manner described with successive MKpulses causing the odd and even tubes to be fired alternately.

By means which do not form a part of this invention a sixty-five voltpulse is applied to the SP lead periodically, or at the end of eachseries of MK pulses. Techniques for providing such pulses are Well knownto those skilled in the art and, therefore, are not shown herein. It isevident that an SP pulse may be applied after any number of MK pulses.That is, the SP pulse may occur when either contacts 502 or 563 areclosed. The application of an S? pulse will be used to reset the drivercircuit and to reset the counter circuit and/or to shift the connectionsthrough a steering circuit so that the information represented by asubsequent series of pulses will be registered in another register.Obviously, the driver circuit may or may not happen to be in its resetcondition at the time of the occurrence of the SP pulse. The resetcondition of the driver circuit is with contacts 562 closed. If thedriver is already in its rest condition, there is no need for the SPpulse to alter the drive circuit of FIG. 1. However, if the drivecircuit must be reset by the SP pulse, the drive circuit must beprevented from providing another pulse to the counting circuit.

The pulse applied to the SP lead Will be conducted to the starter anodesof tubes 4% and 2122. However, if the driver circuit is already in thereset condition, i.e., if contacts 5492 are closed, then the SP pulsewill not fire either of the tubes 4% or 222, but the SP pulse will beapplied through capacitor 433 to the Reset lead to the counter circuit.f a plurality of registers are used, the SP pulse on the Reset lead canbe applied to a steering circuit to cause the digital informationcounted by the counter to be transferred to a selected one of theplurality of registers. If the driver is not already in the resetcondition, contacts 5&3 will be closed, thereby applying the 3+potential to the anodes of tubes 4% Therefore, upon the application ofthe SP pulse to the starter anodes of these tubes, they will both berendered conducting and relay coil 5% will be energized to open andclose contacts 593 and 5%, respectively.

' lead.

With tube 400 conducting, its cathode will be raised to approximatelya,.sixty-fi-ve volt positive potential, thereby Charging capacitor 431,which will tend to maintain the upper terminals of resistors 405, 406and 407 at this potential after the B+ potential is removed from theanodes of tubes400 and 222. The resistor 421 is employed to keep thecathode of tube 400 from rising volt pulse, which is passed throughcapacitor 430, tends to increase the charge on capacitor 432, therebypassing a pulse on the Reset lead.

Since tube 400 had not been rendered conducting before contacts 502closed, diode 444 had been effectively back biased by the plussixty-five volt potential connected at resistor 715 and, therefore, nopulse below sixty-five volts can be transmitted to the Reset leadthrough capacitor 432. However, when tube 400 fires, a sixty-five voltpotential will also be applied to the junction of capacitor 432 anddiode 444 through resistor 406, thereby nullifying the back bias ondiode 444 and thereby permitting the transmission of pulses to the Resetlead.

Detailed Description Counting Circuit FIG. 2 illustrates a typicalcounting circuit of a type which might be driven by the pulse repeatero-fFlG. 1. As with FIG. 1, the elements of FIG. 2 which have similarfunctions have been given three digit designations with the last twodigits identical. As has already been shown, the pulse repeater of FIG.1 starts in its reset to the driver, the B-{- pulse is maintained on, orshifted in response to a; first pulse on the MK lead, shifts the B+potential to the CAB lead and applies a sixty-five volt pulse to theOPlead. In response to the next pulse on the MK lead, the B+ potentialis shifted back to the EAB lead and a sixty-five volt pulse is, appliedto the EP In response to a pulse applied to the SP lead to the driver,the B+ pulse is maintained on, a shifted to, the EAB lead, but no pulseis applied to the EP lead.

the Reset lead.

It will be assumed for'the present that the Home tube 600 of thecounting circuit has already been fired and that the B+ potential isapplied to the EAB lead. It will be seen later that this is theconditionwhich prevails after a reset pulse.

.Theresistors 601 and 602 are selected as a voltage divider so that whentube 6% is conducting the common point of the two resistors is at asixty-five volt potential. It should be recalled that the tubes haveapproximately a sixty volt anode-to-cathode potential when conducting.The pair of resistors connected between ground and the cathode of eachof the tubes of FIG. 2 have the same function as resistors dilland 602and, therefore, when their respective tube is conducting, the commonresistor point is at a sixty-five volt potential.

When the driver circuit removes 13+ potential from the EAB lead, theHome tube 6&0 is extinguished, but the .charge 'on-capacitor 60dmaintains the common point anodeof the diode 637 is at ground potentialsince no current is flowing in resistors 621, 622 and 623.

ever, the back bias on diode 617 has been nullified by .virtue of thepotential across resistors 601 and 602 from Howcharged capacitor 604.That is, the anode and the cathode of diode 617 are both at a plussixty-five volt potential a The SP pulse is either applied directly orrepeated to v 6 and, therefore, the starter anode of tube 610 is at aplus sixty-five volt potential. Accordingly, the application of thesixty-five volt pulse to the OP lead will pass through capacitor 613 anddiode 617 to raise the potential of the starter anode oftube 610 to onehundred and thirty volts which will cause the tube 610 to tire and startconducting. The firing of tube 610 causes capacitor 614 to be chargedand thereby nullifies the back bias of diode 62.7, which had been backbiased in the same manner as diode 637. Accordingly, when the 13+potential is removed from the CAB lead and applied to the EAB lead, thetube 620 will be enabled to be fired upon receipt of a sixty-five voltpulse on the EP lead. The removal of the B] potential from the anode ofa conducting tube provides a positive extinguishing of that tube.

In this manner, each of the successive tubes in the counting circuit ofFIG. 2 are sequentially fired and extinguished. FIG. 2 may include asmany stages as desired and they may be ring connected and coupled toanother counting unit which records thenurnber of completed rings thathave been advanced through in response to the alternate pulses on the OPand EP leads.

When a pulse is applied to the SP lead in FIG. 1, the B+ potential isconnected to the EAB lead, if it is not already so connected, and asixty-five volt pulse is applied to the Reset lead. If at the time of anSP pulse the B+ pulse is on the CAB lead, then the removal of the 13+potential from the CAB lead to transfer it to the EAB leadwill'extinguish whichever one of the odd tubes which had beenconducting. if the B+ potential is on its anode is approximately sixtyvolts above the cathode potential and, therefore, the potential of theEAB lead is momentarily pulled down from the B+ potential to a potentialof approximately sixty volts. The increased current through the commonanode resistor 221 also facilitates the reduction in the potential onthe EAB lead. With the potential of the EAB lead reduced toapproximately sixty volts, the even tube which had been conducting willbe extinguished as the potential of the anode thereofis momentarilyreduced below the potential required to sustain conduction. For example,if even tube 620 has been fired, its cathode capacitor 624 is charged toa potential of approximately seventy-five volts and, therefore, when thepotential of the EAB lead is temporarily reduced significantly below onehundred and sixtyfive volts, the even tube will be extinguished as thepotentiai between the anode and cathode will be reduced below the valuerequired to sustain conduction. As already stated, the Honte tube doesnot react in the same manner as its cathode capacitor 604 is notcharged. Accordingly, in response to the application of an SP pulse tothe driver circuit, the counting circuit is restored to its starting, orreset, condition irrespective of'whether the last tube that had beenfired was an odd or even tube.

When 5823-type' tubes are employed, the following values have been foundto give satisfactory results:

Value 47 Element designation and/or function:

562-, N2, 202, 6%5, 615, 625, 635 kilohms All resistors connected to.+65 volt potential,

lthough the purpose of some elements may not have been described indetail, it is believed that their function will, for the most part, beevident from their similarity to other elements which have beendescribed. The remaining elements form obvious current limiting,clamping, or discharge circuits which are all obvious and well known tothose skilled in the art to which this invention pertains.

While there has been shown and described what is considered at presentto be the preferred embodiment of the invention, modifications theretowill readily occur to those skilled in the art. it is not desired,therefore, that the invention be limited to the embodiment shown anddescribed, and it is intended to cover in the appended claims all suchmodifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. in a pulse repeater, first and second devices each having an anode, acathode, and a stanter anode, a source of pulses having a predeterminedminimum potential with respect to a reference potential, a bistabledevice, first circuit means for applying the pulses from said source tothe starter anodes of both of said first and second devices, saidbistable device including conlrol means for rendering said first deviceconductive in response to the application of one of said pulses to itsstarter anode only when said bistable device is in a first of its stablestates and for rendering said second device conductive in response to anapplication .of one of said pulses to its starter anode only when saidbistable device is in a second of its bistable states, second circuitmeans coupled to said first and second devices for setting said bistabledevice to its first and second states when said second and firstdevices, respectively, are rendered conducting, first and second outputterminals, and means for producing an output pulse at said first andsecond terminals in response to the setting of said bistable device toits first and second states, respectively, whereby pulses arealternately applied to said first and second terminals in response tosuccessive pulses from said pulse source.

2. The combination as set forth in claim 1 and including a second sourceof pulses having a predetermined minimum potential with respect to areference potential, circuit means for applying pulses from said secondsource to the starter anode of said second device, said control meanscontrolling said second device for rendering it conductive in responseto the application of a pulse from said second source to its starteranode only when said bistable device is in the second of its bistablestates, whereby said bistable device is set to a predetermined one ofits stable states'in response to each pulse from said'second source.

3. The combination as set forth in claim 2 and including a third devicesimilar to said first and second devices, circuit means for applyingpulses from said second source to the starter anode of said thirddevice, said control means controlling said third device for renderingit conductive in response to the application of a pulse from said secondsource to its starter anode only when said bistable device is in thesecond of its bistable states, and means coupled to said third deviceand a selected one of said output terminals for inhibiting theproduction of an output pulse on said selected terminal when said thirddevice was rendered conductive.

4. The combination as set forth in claim 3 wherein any one of saidfirst, second, and third devices which is rendered conductive inresponse to the application of a pulse from either of said pulse sourcesto their respective starter anodes is rendered non-conducting inresponse to the shifting of said bistable device from one of its stablestates to the other of its stable states.

5. The combination as set forth in claim 4 wherein said bistable devicecomprises an electromechanical device.

6. In a pulse repeater, first and second devices each having an anode, acathode, and a starter anode, a source of pulses having a predeterminedminimum potential with respect-to a reference potential, a bistabledevice, first circuit means for applying the pulses from said source tothe starter anodes of both of said first and second devices, saidbistable device including control means for rendering said first deviceconductive in response to the application of a pulse to its starteranode only when said bistable device is in a first of its stable statesand for rendering said second device conductivein response to anapplication of a pulse to its starter anode only when said bistabledevice is in a second of its bistable states, second circuit meanscoupled to said first and second devices for setting said bistabledevice to its first and second states when said second and firstdevices, respectively, are rendered conducting, a two-terminal source ofpotential, first and second output bus leads, and a selected one of saidtwo terminals of said potential source connected to said control meansfor connecting said selected terminal to said first and second bus leadswhen said bistable device is set to its first and second states,respectively, whereby the potential of said one terminal is alternatelyconnected to said buses in response to successive pulses from said pulsesource.

7. The combination as set forth in claim 6 and including a second sourceof pulses having a predetermined minimum potential with respect to areference potential, circuit means for applying pulses from said secondsource to the starter anode of said second device, said control meanscontrolling said second device for rendering it conductive in responseto the application of a pulse from said second source to its starteranode only when said bistable device is in the second of its bistablestates, whereby said bistable device causes the selected one of said twoterminals of said potential source to be connected to a predeterminedone of said buses in response to a pulse from said second source.

8. The combination as set forth in claim 7 and including a third devicesimilar to said first and second devices, circuit means for couplingpulses from said second source to the starter anode of said thirddevice, said control means controlling said third device for renderingit conductive in response to the application of a pulse from said secondsource to its starter anode only when said bistable device is in thesecond of its bistable states, a pulse output lead, and means coupled tosaid third device and said pulse output lead for inhibiting an outputpulse on said pulse output lead until said third device is renderedconductive.

9. The combination as set forth in claim 8 wherein any one of saidfirst, second, and third devices which is ren dered conductive inresponse to the application of a pulse from either of said pulse sourcesto their respective starter anodes is rendered non-conducting inresponse to the shifting of said bistable device from one of'its stablestates to the other of its stable states.

10. In a driver for controlling a counting circuit, first and secondtubes having an anode, a cathode, and a control anode, a bistabledevice, a given potential, first circuit means for selectively applyingsaid given potential between the cathode and anode of said f'n'st tubewhen said bistable device is in its first stable state and forselectively applying said given potential between the cathode and anodeof said second tube when said bistable device is in its second stablestate, a source of driving pulses, coupling means for coupling pulsesfrom said source to both of said control anodes, said first tube beingresponsive to the coupling of a pulse to said control anodes forproviding a current in the anode-cathode circuit of said first tube whensaid bistable device is in said first state, said second tube beingresponsive to the'coupling of a pulse to said control anodes forproducing a current in the anode-cathode circuit of said second tubewhen said bistable device is in said second state, and second circuitmeans responsive to the current in the anode-cathode circult of saidfirst and second tubes, respectively, for switching said bistable deviceto its second and first states, stable device is set to a predeterminedone of its bistable respectively. states in response to each pulse fromsaid second source.

11. The combination as set forth in claim 10 and including a secondsource of driving pulses, coupling means References Cited in the file ofthis patent for coupling pulses from said second source to the con- 5 1UNITED STATES PATENTS trol anode of said second tube, said second tubebeing responsive to the coupling of a pulse from said second 2,059,562Curtis 1936 source to its starter anode for producing a current in2,837,701 June 3, 1958 the anode-cathode circuit of said second tubewhen said 29641587 Eakm 1960 bistable device is in said second state,whereby said bi- 1o

1. IN A PULSE REPEATER, FIRST AND SECOND DEVICES EACH HAVING AN ANODE, ACATHODE, AND A STARTER ANODE, A SOURCE OF PULSES HAVING A PREDETERMINEDMINIMUM POTENTIAL WITH RESPECT TO A REFERENCE POTENTIAL, A BISTABLEDEVICE, FIRST CIRCUIT MEANS FOR APPLYING THE PULSES FROM SAID SOURCE TOTHE STARTER ANODES OF BOTH OF SAID FIRST AND SECOND DEVICES, SAIDBISTABLE DEVICE INCLUDING CONTROL MEANS FOR RENDERING SAID FIRST DEVICECONDUCTIVE IN RESPONSE TO THE APPLICATION OF ONE OF SAID PULSES TO ITSSTARTER ANODE ONLY WHEN SAID BISTABLE DEVICE IS IN A FIRST OF ITS STABLESTATES AND FOR RENDERING SAID SECOND DEVICE CONDUCTIVE IN RESPONSE TO ANAPPLICATION OF ONE OF SAID PULSES TO ITS STARTER ANODE ONLY WHEN SAIDBISTABLE DEVICE IS IN A SECOND OF ITS BISTABLE STATES, SECOND CIRCUITMEANS COUPLED TO SAID FIRST AND SECOND DEVICES FOR SETTING SAID BISTABLEDEVICE TO ITS FIRST AND SECOND STATES WHEN SAID SECOND AND FIRSTDEVICES, RESPECTIVELY, ARE RENDERED CONDUCTING, FIRST AND SECOND OUTPUTTERMINALS, AND MEANS FOR PRODUCING AN OUTPUT PULSE AT SAID FIRST ANDSECOND TERMINALS IN RESPONSE TO THE SETTING OF SAID BISTABLE DEVICE TOITS FIRST AND SECOND STATES, RESPECTIVELY, WHEREBY PULSES AREALTERNATELY APPLIED TO SAID FIRST AND SECOND TERMINALS IN RESPONSE TOSUCCESSIVE PULSES FROM SAID PULSE SOURCE.